ASD varies widely in severity and symptoms and may go unrecognized, especially in mildly affected children or when it is masked by more debilitating handicaps. Very early indicators that require evaluation by an expert include:

no babbling or pointing by age 1no single words by 16 months or two-word phrases by age 2no response to nameloss of language or social skillspoor eye contactexcessive lining up of toys or objectsno smiling or social responsiveness.Later indicators include:

impaired ability to make friends with peersimpaired ability to initiate or sustain a conversation with othersabsence or impairment of imaginative and social playstereotyped, repetitive, or unusual use of languagerestricted patterns of interest that are abnormal in intensity or focuspreoccupation with certain objects or subjectsinflexible adherence to specific routines or rituals.Health care providers will often use a questionnaire or other screening instrument to gather information about a child’s development and behavior. Some screening instruments rely solely on parent observations, while others rely on a combination of parent and doctor observations. If screening instruments indicate the possibility of an ASD, a more comprehensive evaluation is usually indicated.

A comprehensive evaluation requires a multidisciplinary team, including a psychologist, neurologist, psychiatrist, speech therapist, and other professionals who diagnose children with ASDs. The team members will conduct a thorough neurological assessment and in-depth cognitive and language testing. Because hearing problems can cause behaviors that could be mistaken for an ASD, children with delayed speech development should also have their hearing tested.

Children with some symptoms of an ASD but not enough to be diagnosed with classical autism are often diagnosed with PDD-NOS. Children with autistic behaviors but well-developed language skills are often diagnosed with Asperger syndrome. Much rarer are children who may be diagnosed with childhood disintegrative disorder, in which they develop normally and then suddenly deteriorate between the ages of 3 to 10 years and show marked autistic behaviors.